Radio direction finder



ct. l0, 1950 T. H. CLARK l l2,524,768

RADIO DIRECTION FINDER Filed Deo. 16, 1944 3 Sheets-fSheel: 1

600A/YE Oct 10 1950 T. H. CLARKr RADIO DIRECTION FINDER :s sheets-sheet 2 Filed neg. 16;. 19144 I i l I I l lli ROTARY HNGLES A TTOENE'Y Oct. 10, 1950 T. H. CLARK 2,524,768

RADIO DIRECTION FINDER Filed Dee. 16, "1944 3 Sheets-Sheet 5 ,/f 108 Hf 10e 62 v l A4 Al 657 Ik flz-l B+ INVENTOR.-

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TYUJP/VE Y Patented Oct. 10, 1950 UNITED STATE-s: enreNr OFFICE RADIO IDIRECTIQNFINDERF Trevor H. Clark, New York,-YN.Y., assignorto.

Federal Telephone and Radio Corporation, vNew' York, N. Y., a corporation.:ofDelaware Application December 16, 19fii, Serial No., 568,461 K This invention relates to radio direction nders t and more particularly to radio directionlnders of the amplitude comparison type.

In radio direction nders of the amplitude comparison type, an indicator is used tovproduce directional indications dependent upon/the' afmplitude of signals received ontwo or more'di're A' tive antennas from a transmitting source, the d1 rection of which is to be determined.L vA simple'v form of amplitude comparison, direction inderv 1U indicator is of the type Wherein crossed loop antennas are arranged foralternate coupling to4 an instrument sothat the energy received in the two loops may be directly compared. It is, however, desirable in many installations to provide 10 separate antennas for receiving energy fromdifferent directions, the antennas being shielded from one another. Such systems are particularly desirable on board ships or aircraft in whichthe f metal structures of the craft themselves may 20 tend to produce errors in directional indications in the normal type of direction finder. When a plurality of such antennas vare arranged to cover separate sectors of an arc, the directional indications normally are substantially the same within each sector covered by two of the antennas. Accordingly, the sense of direction is not clearly indicated. For, example, in.k thetcase of four antennas similar indications would/occurl in each of four quadrants. 4 f 30 It is an object of my invention to provide aL direction finder of the type wherein a plurality of separate unidirectional receiving antenna; collectors are used in adirection nder circuitV to produce amplitude comparison directional in# 35 dicatons and in which means is provided'to indicate the sense of the direction'l within eac-'1i of the sectors defined by the adjacent antennas It is a further object of my inventionto lprovide an amplitude comparison indicator ofthe i0 type dei-ined above usingY anloscilloscop'e i'ndi-'- cator.

It is a further object of my invention to .provide an amplitude comparison indicatorlofthe.. type outlined above using an oscilloscope indicator provided with switching vcircuits to assura that the directional indications are produced :on the oscilloscope screen in positions cclgrpgnfiflg, to the angular diretipnel positioned' mittel' from which energy is received.`

According to a feature of my invention, a plu-f.

ralit'yf of unidirectional antennas are provided,

ofthejse antennas having such a directivey patternfthatthe directive'patterns of adjacent antennas overlap, but those of alternate antennas are 'mutually exclusive. a consequence, the

adajcent antennas of the system provide sectors withinwhich the direction toward an object may be' obtained byamplitude comparison. Further means is provided-sequentially to vcouple the ani y f l i tenna'sfto the'directionlnding receiver arrangement'so that the 'entire farc dened by theseti ofantennas vvillbe scanned atv the predeterminedrate; l The 'coupling'means for each of V'the' antennas is adjusted'to' provide coupling during the periodcorresponding tothe scanning oi the sec-VK tor covered by thel directive pattern of the particular antenriav.

Alternatequadrantal` antennas may be coupled togethery to vthe receiving equipment 'since the' reception patterns of thesealternate antennas are mutually exclusive. Preferably afchopping circuit-is provided-in the coupling means to alternately couple the alternate antennas to the receiver.) The output from the adjacent an-A tennas is then appliedto an amplitude compari son. indicator to provide a directional indication/"The indicator is also providedvwith a sweep circuit which willsweep an indicating beam about a/circle in synchronism with the successivecouplingof tlnieantennas.` The incoming signals pro-y dujiia 'radiall deflection of :the beam, the radial deflectionbecoming z ero when signals fromadjacent 'antennas are equal! Accordingly, on'v the face of the indicator Will be provided an indica-jtion' pointing toward any station from which en-v A better understanding oi my invention and` n theobjects and vfeatures thereof. may` be. had by reference to the particular descriptionof an emv;

ateihes bodiment thereof made with reference to the accompanying drawings, in which:

Fig. 1 is a schematic circuit diagram of a direction finder incorporating the features of my invention;

Fig. 2 is a graphical representation of the switching cycle of the direction finder of Fig. l;

Fig. 3 is a diagram indicating the patterns produced in different quadrants of the direction finder of Fig. l; and

Fig. 4 is a diagram of a modification to Fig. l to produce the results indicated in Fig. 3.

Turning rst to Figs. 1 and 2 oi the drawings, four antennas are shown, i, 2, 3 and 4, each antenna being unidirectional and shielded from the other antennas as indicated by the dotted line shields shown at t, l and B. The pattern from each of these antennas is preferably substantially circular and tangent to the respective reflectors so that the patterns of adjacent antennas such as I-2, 2 3, 3-4, and 4l will overlap but the patterns of alternate antennas such as l relative t 3 and 2 relative to 4, are mutually exclusive. Thus, energy incoming from a given direction, as indicated at E for example, will be effective on only two of these antennas, for example antennas l and 2, and will not be effective on the other antennas. Furthermore, while I have shown four antennas in the illustrative embodiment, any number of antennas may be provided so long as the patterns oi alternate antennas do not overlap while those of adjacent antennas do.

The switching circuit or generator l is provided for alternately coupling antennas l and 3 and 2 and 4 to a receiver circuit il. The output of receiver l is applied through separate amplifiers l2 and I3 and line I4 to an indicator shown generally at i5. This indicator is preferably in the form of an oscilloscope as shown. The beam of the oscilloscope is swept around the screen I6 thereof in synchronism with the switching operation performed by switching circuit i0 so that the position of the beam on the screen will correspond in angular relationship to the angles about the direction finder.

Switching or antenna coupling circuit l@ may comprise any desired form of switching wave generator but as shown in the drawing, the generator includes the resistance block i1 `similar to that described in more detail in my copending abplication, Serial No. 526,290, iled March 13, 1944, Patent No. 2,402,603, granted June '25 1946. A pair of conductors I8 and i9 are connected to opposite sides of block Il' and. are supplied with energy from a square wave or chopping generator.

20. A pair of brush arms 2i and 22 are mounted in contact with the resistor plate il. Vlhen rotation between plate il and arms 2i, 22 occurs, the voltages between the arms 2l, 22 and ground will follow generally a sine wave form and are displaced from one another in phase quadrature. The period of generator 2i) is relatively short with respect to the period of a complete rotation of the arms. Since the square wave generator 2,0 provides a chopping action of the voltage applied between the conductors I8 and ES, these sine waves will be broken up into a plurality of small Waves as can be more readily appreciated by re ferring generally to Fig. 2. Brushes 2l and 22 are connected to lines 23 and 24, respectively, for uti lizing the voltage developed in switching generator I0 for the purposes outlined more particularly hereinafter.

Each of the antennas l, 2. t and 4 is provided with a corresponding coupling tube 25, 26, 2'!

. tion of energy applied thereto.

lli

(ifi

4 Y and 28. These tubes are chosen with substan-l tially similar characteristics so that they will be similarly effective in their blocking action controlled by the output waves from switching generator it and will all produce similar amplifica- Antenna l is coupled over a condenser 29 to control grid 30 oi tube 25. Grid 30 is normally biased to cut-orf by means of a biasing battery 3! Potential from switching circuit lil is applied over line 23, line 32 and choke coil 33 to the cathode 34 of tube l. The potential applied to this cathode 34 serves to alter the bias of grid 30 relative to the cathode. Thus when the potential applied is negative, the

bias of battery 3l will be overcome so that the tube will be conductive, and output energy from antenna i will be coupled over condenser 35 and lines 36 and 3l to the input of receiver H.

The antenna 3 which is the alternate antenna to antenna i is coupled similarly through a condenser 33 to the control electrode 39 of tube 21. Grid 39 is also negatively biased and is connected in series through line 40 to line 23. As a consequence, negative voltage applied to the grid of tube 21 will have no eiect on unblocking the tube but positive potential applied thereto will tend to neutralize the negative bias so that antenna 3 will be coupled through condenser 4l, line 42 and line 31 to the input of receiver l l. Because of the square wave generator voltage applied across conductors l and i9, it will be seen that antennas I and 3 may be coupled over the same line 3'! to receiver li. Since these antennas will normally never simultaneously receive energy from the same source, they may be interconnected in the manner shown without dfculty.

Antennas 2 and 4 are similarly coupled over tubes 25 and 2S to the transmission line '24, coupled to brush 2.2. Because of the right angular relationship of brushes 2l and 22, it will be clear that the voltage in line 24 will be in phase quadratirre to the voltage in line 23. As will be seen from the subsequent description, the voltages from antennas 2 and 4 are applied to receiver Il, during the intervals between the pulses from antennas and 3.

Antenna 2 is coupled through a condenser 44 to a grid 46 of the tube 26. Grid 46 is maintained negatively biased by battery and is coupled over lines l? and 24 to brush 22. As a Iconsequence positive voltage will serve to unblock tube 26 permitting energy from antenna 2 to be applied over lines 48 an-d i9 to the input of receiver Il.

Antenna 4 is coupled over condenser 50 to control grid 5I of tube 28. The grid of this tube is likewise biased to cut-off. The output from brush 22 of generator ID, however, is applied over line 52 and choke coil 53 to cathode 54 of tube 28 so that the tube is unblocked only by the application of negative potential thereto. It will thus be seen that as` generator i0 operates to produce the sine wave switching voltages, antennas I, 2, 3 and 4 Will be sequentially coupled to receiver II. In the output of receiver H the two amplifiers I2 and I3 are arranged to be unblocked alternately at the rate of the Waves from generator 20 by voltages from brushes 2l and 22 over lines 23 and 55 and 24 and 5S, respectively. Ii necessary, depending upon the relative frequencies of the waves from generator 2E! and generator I0, a delay means 43 may be provided, which serves to shift the energy in line 24, one-half the period of the square waves from generator l0, to assure that these voltages will be applied to the receiver Il during the interval between the voltages applied I to the receiver through line- 31. Thusv Output from one antenna passes through the receiver at a time; iirst the antenna outputs I and 2 areal'- ternately passed through the receiver at the relative fast rate of the waves from 20 then 2 and 3, 3 and l and I, the groups I and 2', 2 and 3,

and 4, i and i, being switched at the relatively slower rate of the waves from generator =I 53. M

The output energy from ampliers I2 and I3i is combined in phase opposition at juncture 59, the output from one of the 'ampliiiers i2, for example, being delayed in delay network 53 by an amount equal to one-half 'of the period vof the square Wave switching voltage so that these outputs will be combined in phase opposition. This output voltage is then applied over line vHI to a second sine wave generator 59 which may befsimilar in construction to generator Ifi. Generator Turning now to Fig. 2, the operation ofthe system of Fig. 1 will 'be more fully described. As pointed out above, antennas I, 2, 3 and 4 are sequentially coupled to the receiver circuit. However, assuming energy is incoming in the quadrant defined by antennas I and 2 then the voltage i applied to vertical electrodes 65 and $5 will be only the output voltage from antennas I and 2. Thus, in this quadrant, energy indicated at 69 in antenna I will vary between a maximum value shown in curve a to zero value as shown in curve y as the direction of received energy varies from a direct line on the antenna I to a direct line on the antenna 2. Similarly, the energy received on antenna 2 shown at 'f will vary from a zero value in curve a to a maximum value as shown in curve g. Since the outputs from these two antennas are combined in phase opposition, the energy will reduce to zero at successive points indicated at 'II through 'Il as shown in the respective curves a to g of Fig. 2. Thus, on the screen'of the oscillograph I5 the zero pointing indication "i8 (Fig. 1) will move from zero point adjacent plate 'Si counterclcckwise to the 90 indicating position adjacent plate 65.

In the succeeding quadrant covered by anten'- nas 2 and 3, the energy on antenna 2 will again vary in the manner shown by curve 'I0 of Fig. 2. However, the energy incoming-on antenna 3 will vary in the manner shown in curve 'I9 of Fig. 2 from a maximum in curve a to a minimum `in curve g. The zero balance point will therefore vary as shown at "EI, and 80 through 85 of Fig. 2 so that the pointing indicator 'I8 will tend to rohave toftecaiibratee 'in a peer-111er iasiiiori as Y shown in rig. 1f 'unless other provisions are made to take carevof this discrepancy. Y

VTurningto Fig. 3there is shown afseries of cathode ray indicator screens 58S, through K9 c i1- lustrating the variation in the pointer indications 'following clockwise' around the phase of the in'- dicator dial -f-or the various angles of reception.

This result, may be accomplished by lcoul'olir'ig 'antennas I and 3 Aacross the horizontal plates and antennas 2 vand 4' across the :vertical plates for jtlre first quadrant indicated at 9i, Fig. 3; cou- 'nasjand- 2 Vcoupled across the vertical electrodes for quadrant' 99, and 'coupling antennas I'landf across "the vertical and Vantennas Il andiiacross tate in a clockwise direction from apos'iti'on'adrant as indicated by curves 8S and 69 of Figf'Z.

'As a consequence, the 'osciilographindicatcr'wnl fthe horizontal Ielectrodes for Acm'adumt `I an'.

' To accomplish 'this result, s switching' disc may be added to the circuit arrangement or Fig. i 'as l 'indicated in the diagram of Fig. 4'. Thisswitchtat'ion between discIIlI and brushes I 4Iilvlto VI I3 is y vproduced synchronously with rotary generators flil and 59 of Fig. 1 so -that the connections to 'vertical plates '65, -63 and horizontal plates 65,

68 are alternately coupled to brush arms 62 and 6310i 'generator 59. Thus, a shift in position of the normal beam pattern occurs on each successive-quadraritof the indicator 'I5. Because-of this switching arra'nger'nent then the pointer maybe made to traverse clockwise around the dial in accordance with vthe various directions of reception 'at a substantially vuniform rate. v

It is clear that the s'ame'eiect-may beobtained by othermeans, such as switching the antenna inputs if desired instead of switching at the indicator.- lI-Iowever,tl-ie switching circuit lin the indicator is fsubstaiitialliy simpler 'thanthe vari-- ation in'coupling on 4theswitching arrangement that would be necessary in the output of the Vreceiver vto accomplish a similar result.

It should lbe yclear that while I-have `described particular Vtypes fof `vol-tage .generator-s to control the .Y various switching operations, any suitable switching wave generators may be used forv this Likewise, any desired type of'chopper lor square wave circuit vmay Ybe used to effect the V.switching operation if this -isfalso considered desirable. 'Moreover, the circuit may be used as va direction finder without the square Wave chopping effect. It should be understood that the speed of rotation of the Yvarious generator4 arrangements Vis not material Vto the operation of thecircuit butshould be suiiiciently highso that apersistent vision on thecathode ray-screen will be obtained. Moreover, for rapidly moving Yobjects it is desirable that the direction `finder operateat a higher'rate of speed than is :necessary with relatively slow moving objects.

"It should be distinctly understood that the specificefxamples of my invention described above in .connectionwith a, particular .circuit aregiven merely "by 'way of 'example `and Ashould not Abe Th'e'oppo'site Aends of brush armv 5-2 are cou-.-

considered as a limitation on the scope of my invention as set forth in the objects thereof and in the accompanying claims.

I claim:

l. A direction finder comprising four unidirectional antennas arranged to receive energy over directive patterns such that patterns of alternate antennas are mutually exclusive, an indicator circuit, a receiver, means for alternately coupling the first and third of said antennas to said receiver at a slow rate, means for alternately coupling the second and fourth of said antennas to said receiver at said slow rate, means for sequentially rendering the coupling means for said antennas eective at a rapid rate so that energy received on an odd numbered and an even numbered antenna is successively applied to said receiver and means for comparing pairs of successively received energies to determine the direction of the source of received energy.

2. A direction finder comprising a plurality of sets of unidirectional antennas positioned to receive energy over directive patterns such that patterns of alternate antennas are mutually eX- clusive, a receiver, separate normally ineffective means for alternately coupling at a slow rate the antennas of one set of alternate antennas to said receiver, separate means for alternately coupling at said slow rate the antennas of the other set of alternate antennas to said receiver, means for successively rendering said separate means effective at a rapid rate so that energy from one antenna at a time is applied to said receiver, means for combining in phase opposition pairs of successively received energies to obtain resultant outputs thereof, an oscilloscope indicator having dei'lector means for moving the beam of said oscillcscope in two coordinates, means for producing a rotation of said beam at said slow rate and means for modulating said beam rotation with said resultant outputs to produce an indication of the direction of the source of received signals.

3. A direction nnder comprising a plurality of sets of unidirectional antennas positioned to receive energy over directive patterns such that patterns of alternate antennas are mutually exclusive, a receiver, separate normally ineffective means for coupling the antennas of one set of alternate antennas to said receiver at a low frequency and separate normally ineffective means for coupling the antennas of the other set of alternate antennas to said receiver at said low frequency, means for successively rendering said separate means effective at a high frequency so that energy from one antenna at a time is applied to said receiver, means for combining in phase opposition pairs of successively received energies to obtain resultant outputs thereof, an oscilloscope indicator having two pairs of angularly disposed deiector means, a source of two low frequency waves phase displaced 90 from each other, means for separately modulating said last named waves with said resultant outputs, means for applying said last named modulated outputs to separate deector means for producing an indication of the direction of source of received signals.

l. A direction nder of the type wherein a direction line between the director nder and a transmitting station is indicated within a given sector of an arc comprising a plurality of sectors in response to energy transmitted from said station and received by directive antennas located substantially at the boundaries of said sectors, the directive patterns of each antenna overlapping only a portion of the directive patterns of the next adjacent antenna, a receiver, means for combining the energy received by diiferent groups of said antennae to provide separate combined outputs corresponding to the number of sectors in said arc, each of said combined outputs comprising alternate samplings of the energy received by the antenna comprising ya group, means for applying said combined outputs sequentially at a given rate to said receiver, means for comparing the amplitude of successive pairs of samplings of each group in said receiver output to obtain compared outputs corresponding to each group, an indicator, means for applying each of said compared outputs to said indicator for indicating from which sector the energy is received,

5. A direction finder of the type wherein a direction line to a ltransmitting station is obtained from energy transmitted from said station and received by adjacent antennas of a plurality of directive antennas, the directive patterns ofalternate antennas V'being mutually exclusive whereby the received energy in any adjacent antennas define a predetermined sector in an arc defined by the directive patterns, comprising a receiver, a source of high frequency switching signais, a source of low frequency switching signals, means for modulating said high frequency signals with said low frequency signals to obtain resultant switching signals of different phase, means for modulating one mutually exclusive pair of antenna outputs in phase opposition with said f resultant signals of one phase and means for modulating another mutually exclusive pair of antenna outputs in phase opposition with said resultant signals of a phase different from said one phase, means for applying said modulated waves to said receiver comprising means for phasing said modulated waves whereby each antenna output is passed separately through said receiver, means for combining the antenna outputs corresponding to a successively received pair of antenna outputs, an indicator, means for applying said combined outputs to said indicator for comparing the amplitudes thereof.

6. An arrangement according to claim 5, wherein said combined outputs are compared for a full low frequency cycle of modulation.

7. An larrangement according to claim 6, wherein said antennas comprise four quadrature spaced antennas, said resultant switching signals comprising waves phase displaced at said low frequency.

8. An arrangement according to claim '7, wherein said indicator comprises a cathode ray tube having deflection means, a source of two low frequency waves phased displaced 90 from one another, means for modulating said combined outputs with separate ones of said last named waves to obtain separate outputs, means for applying said separate outputs to separate deflection means for indicating from which sector the energy is received.

9. A direction finder of the type wherein successive comparison in amplitude is made between the energy received from a radio wave source by adjacent pairs of uni-directional antennas, a plurality of said antennas being positioned to receive energy from substantially all directions about said direction finder, a receiver, means for selecting a pair of antennas, means for alternately applying at a relatively rapid rate the antenna outputs of a selected antenna pair to said receiver, means for cyclically varying the antenna pairs selected at a relatively slow rate, means for comparing the receiver outputs corresponding to successively received pair of antenna outputs to obtain a resultant output thereof, indicator means, means for lapplying said resultant outputs successively to said indicator.

10. An arrangement according to claim 9, wherein said means for comparing comprises means for combining the antenna outputs in phase opposition.

TREVOR H. CLARK.

REFERENCES CITED The following references are of record in the file of this patent:

Number Number 10 UNITED STATES PATENTS Name Date Busignies Dec. 31, 1929 Brunner June 11, 1940 Earp Sept. 3, 1940 Wagstaife Sept. 3, 1940 Neufeld Sept. 10, 1940 Steinhoi Jan, 8, 1946 Busignies Sept. 24, 1946 Yiront-IIGN PATENTS Country Date Great Britain Apr. 29, 1937 

